PID controller and probe

[AJ_Rowley]

Hey guys,

This is for you technical heads who understand how PIDs work. I have been thinking of making a PID controller for my HLT and got thinking why not use it for my boil kettle as well.

Now I'm going to be using 2 kettle elements in each vessel. What I'm wondering is, if I was to have 1 pt100 probe connected to each vessel but have an xlr connector to the control box would I be able to use 1 PID controller.

Basically my plan is heat strike water and sparge with the first probe from HLT. Then disconnect that probe and connect the probe from the boil kettle.

[biertourist]

Hey guys,

This is for you technical heads who understand how PIDs work. I have been thinking of making a PID controller for my HLT and got thinking why not use it for my boil kettle as well.

Now I'm going to be using 2 kettle elements in each vessel. What I'm wondering is, if I was to have 1 pt100 probe connected to each vessel but have an xlr connector to the control box would I be able to use 1 PID controller.

Basically my plan is heat strike water and sparge with the first probe from HLT. Then disconnect that probe and connect the probe from the boil kettle.

AJ,

My current system is setup this way.  It's definitely not ideal, but it works OK.

There's a few problems with this setup:
1. The PiD controller's calibration process will be measuring the heat loss and other parameters in whatever vessel / probe the PID is connected to when you do the calibration; these items will be different in a vessel with a different geometry (if you calibrate in the HLT, the PID will be calibrated for the HLT, not the boil kettle)
2. The PID controller's "fuzzy logic" capabilities (if yours has fuzzy logic) further exascerbate the problem as its' constantly measuring how the vessel actually response to adding additional heat and how quickly that heat dissapates and it tweaks how it works to avoid over/under shooting.  -When you switch between vessels you'll majorly confuse the fuzzy logic and your temp will start over and under shooting more and more dramatically over time and then you need to waste a couple of hours recalibrating with water before you brew again...

Personal Opinion: Feel free to build your control panel with a single SSR and heat sink but use a 2 or 3 way switch so that you can switch between PID control and a simple rheostat. -Use the PID for the HLT only and use the rheostat for the boil kettle.  -Then use another analog or digital thermometer to monitor boil kettle temps for chilling.  The PID controller in the boil kettle essentially is just a super expensive thermometer as you just need to monitor temps during chilling; beyond that you just need the ability to control the heat output and a rheostat -type dial that has a PWM circuit is fit-to-purpose.

I'm literally building a 2nd small control panel box that controls my boil kettle with a pwm-based rheostat-style dial and I'm using my existing PID and control panel only for the HLT and MLT recirculation.  I kind of wish I would've gone with 2 PID controllers in the first place, knowing that I was going to HERMS mash eventually. Lesson Learned: Plan for the future with your control panel and don't let this be the thing that you go cheap on because the labor of building one yourself is so intense, it's just not worth having to do it again.


$0.02,
Adam

[AJ_Rowley]

Thanks Adam,

As always an encyclopaedia of knowledge. Nothing bought or made yet, but like yourself I do see myself going Herms in the future.